1. Field of the Invention
This invention is directed to a fluorinated aromatic acetal polymer composition, a method of preparing such a composition, a photosensitive composition which comprises such a polymer composition and a diazo resin, and imageable members such as lithographic printing plate precursors comprising such a photosensitive composition. After imaging, such a precursor is useful as a lithographic printing plate.
2. Background Information
The use of acetal polymers in photosensitive compositions is well known to those skilled in the art, as disclosed for example in: U.S. Pat. Nos. 5,169,897; 5,219,699; 5,262,270; and 5,534,381. However, although photosensitive compositions containing such acetal polymers have generally performed in an effective manner, improvement in terms of enhanced press life of printing plates containing such compositions is desirable. In addition, enhanced water repellency (to retain high image quality by maximizing hydrophobicity with respect to the hydrophilic portions of the composition) and resistance to plate cleaner solutions (to permit plate cleaning without concurrent reduction in image quality) are desirable.
It is also well known to those skilled in the art that photosensitive compositions comprising a diazonium compound and a polymeric binder may be prepared and used in imageable members such as lithographic printing plates. For example, U.S. Pat. No.3,790,382 discloses an oleophilic composition suitable for use as the ink-receptive layer of a printing plate, in which the oleophilic composition comprises a light-sensitive diazo resin, a polyamide resin binder, and a polymer containing a non-aromatic fluorinated component. However, in contrast to the photosensitive composition of the present invention, the oleophilic composition disclosed in U.S. Pat. No. 3,790,382 contains a fluoropolymer component which must be non-aromatic.
It has now been found that photosensitive compositions comprising the novel fluorinated aromatic acetal polymers of this invention and at least one diazo resin advantageously provide enhanced press life, water repellency and resistance to plate cleaner solutions when such photosensitive compositions are employed as part of an imageable element such as a lithographic printing plate. Accordingly, it is an object of this invention to provide this novel fluorinated aromatic acetal polymer. It is another object of this invention to provide a method of preparing such a fluorinated aromatic acetal polymer. It is yet another object of this invention to provide a photosensitive composition comprising at least one diazo resin and at least one such fluorinated aromatic acetal polymer of this invention. It is yet another object of this invention to provide a method of preparing such a photosensitive composition. It is yet another object of this invention to provide an imageable member comprising a support and a photosensitive composition of this invention.
The fluorinated aromatic acetal polymer composition of this invention comprises at least one unit of A and at least one unit of either B or C, or at least one unit of each of A, B and C, and optionally further comprises at least one unit of either D or E, or at least one unit of each of D and E, wherein the units are linked together by single covalent Cxe2x80x94C bonds and have the formulae: 
where A, B, C, D and E are present in the corresponding ratio n1l:n2: n3:n4:n5, where n1=10-80 mole %; n2=0-65 mole %; n3=0-65 mole %; n4=0-50 mole %; n5=0-20 mole %; RA is H or a C1-C11 alkyl group, or an aryl group that does not contain fluorine, and RB and RC are aryl groups that contain fluorine, including (trifluoromethyl) phenyl and fluorophenyl groups. Here an aryl group is defined as any group obtained from an aromatic compound by removing one of the hydrogen atoms attached to an aromatic carbon atom.
In one preferred embodiment, the unit B has the formula: 
where each of R1 and R2 is independently F, H, or an alkyl group. The fluorinated aromatic acetal polymer composition is preferably prepared by the process comprising reacting a hydrolyzed polyvinyl acetate polymer or copolymer with at least one non-fluorinated aldehyde component, and at least one fluorinated aromatic component.
The photosensitive composition of this invention comprises at least one diazo resin, and at least one fluorinated aromatic acetal polymer composition as described above. The imageable member of this invention comprises a support and the photosensitive composition as described above applied to the support. In a particularly preferred embodiment, the imageable member of this invention is used as a lithographic printing plate precursor, and upon imaging is used as a lithographic printing plate.
The fluorinated aromatic acetal polymer composition of this invention comprises at least one unit of A and at least one unit of either B or C or at least one unit of each of A, B and C, and may further comprise at least one unit of either D or E, or at least one unit of each of D and E, wherein the units are linked together by single covalent Cxe2x80x94C bonds and have the formulae: 
where A, B, C, D and E are present in the corresponding ratio n1:n2:n3:n4: n5, where n1=10-80 mole %, n2=0-65 mole %, n3=0-65 mole %, n4=0-50 mole % n5=0-20 mole %, RA is H or a C1-C11 alkyl group, or an aryl group that does not contain fluorine, and RB and RC are aryl groups that contain fluorine, including (trifluoromethyl) phenyl and p-fluorophenyl groups. The non-fluorinated alkyl and aryl groups may be substituted or unsubstituted. Aralkyl groups are particularly preferred.
In a preferred embodiment, and unit B has the formula: 
where each of R1 and R2 is independently F, H or an alkyl group. In a particularly preferred embodiment, R1 and R2 are each F.
In a preferred embodiment, the composition of the invention further comprises at least one acid group having a pKa equal to or less than 11. The acid group is preferably a carboxylic acid group and most preferably is derived from a carboxybenzaldehyde. The composition preferably further comprises at least one photopolymerizable ethylenically unsaturated group, at least one photocrosslinkable group, or a combination thereof.
The fluorinated aromatic acetal polymer composition of this invention is preferably prepared by the process comprising reacting a hydrolyzed polyvinyl acetate polymer or copolymer with at least one non-fluorinated aldehyde component and at least one fluorinated aromatic component. The term aldehyde component includes aldehyde derivatives such as acetals. The reaction conditions which may be used are those that will be well known and understood by those skilled in the art for reacting such components. For example, the components may be reacted at temperatures in the range of from ambient to about 150xc2x0 C., preferably from about 40xc2x0 C. to about 100xc2x0 C., for a period of time ranging from about 30 minutes to about 24 hours, preferably about 2 hours to about 8 hours. Relative to the hydrolyzed polyvinyl acetate polymer or copolymer, the non-fluorinated aldehyde components may be reacted in amounts from about 10 to about 80 mole %; the fluorinated components may be reacted in amounts of from about 5 to about 65 mole %.
In a preferred embodiment, the hydrolyzed polyvinyl acetate polymer or copolymer is prepared as follows. Vinyl acetate is polymerized, or copolymerized with other monomers, to produce a polyvinyl acetate polymer or copolymer. The weight average molecular weight (Mw) of the polyvinyl acetate polymer or copolymer is about 20,000 to about 130,000 g/mole, preferably about 35,000 to about 130,000 g/mole. Vinyl alcohol groups are then produced by hydrolysis of the acetate groups. Acetate groups are hydrolyzed to the extent of about 70-98 mole %, preferably about 80-98 mole %. Other monomers useful in making a copolymer include vinyl esters of C3-C22 carboxylic acids having linear or branched chains and acid-functional monomers, such as crotonic acid.
In a preferred embodiment, the non-fluorinated aldehyde component is selected from the group consisting of at least one of an aliphatic aldehyde, an aromatic aldehyde, an aralkylaldehyde, and a carboxyl-functional aldehyde. In a particularly preferred embodiment, the non-fluorinated aldehyde component is propionaldehyde.
In a preferred embodiment, the fluorinated aromatic component comprises at least one fluoro group, at least one trifluoromethyl group or at least one trifluoromethoxy group attached to the aromatic ring.
In another preferred embodiment, the fluorinated aromatic component is selected from the group consisting of one or more of: 4-fluorophenyl isocyanate; 4-fluorobenzaldehyde; 2,3-difluorobenzaldehyde; 2,4-difluorobenzaldehyde; 2,5-difluorobenzaldehyde; 2,6-difluorobenzaldehyde; 3,4-difluorobenzaldehyde; 3,5-difluorobenzaldehyde; 2,3,4-trifluorobenzaldehyde; 2,3,5,6-tetrafluorobenzaldehyde; pentafluorobenzaldehyde; p-trifluoromethylbenzaldehyde; m-(trifluoromethyl)benzaldehyde, m-(trifluoromethyl)phenyl isocyanate, p-(trifluoromethyl)phenyl isocyanate, 3,5-bis(trifluoromethyl)phenyl isocyanate, 4-(trifluoromethoxy)phenyl isocyanate, 2-chloro-5-(trifluoromethyl)phenyl isocyanate. In a particularly preferred embodiment, the fluorinated aromatic component is p-trifluoromethylbenzaldehyde.
The photosensitive composition of this invention comprises : (1) at least one diazo resin; and (2) at least one fluorinated aromatic acetal polymer composition according to this invention, as described above.
The diazo resin or resins used in the photosensitive composition of this invention may be any diazo resin or resins known to be useful in photosensitive compositions or imaging members such as lithographic printing plates. These include, for example, the condensation product of p-diazo diphenyl amine and paraformaldehyde, the condensation product of 3-methoxy-4-diazo diphenylamine and paraforrnaldchyde, and the diazo resins of U.S. Pat. Nos. 2,063,631; 2,667,415; 2,667,498; 2,922,715; 2,946,683; 3,050,502; 3,163,633; 3,227,074; 3,311,605; 3,406,159; 3,679,419; 3,849,392; and 3,867,147.
The diazo resin is typically employed in an amount of about 10 to about 60 percent by weight of the photosensitive composition, more preferably in an amount of about 20 to about 40 percent by weight. The fluorinated aromatic acetal polymer is typically employed in an amount of about 10 to about 70 percent by weight of the photosensitive composition, more preferably in an amount of about 20 to about 65 percent by weight.
In addition to a diazo resin and the fluorinated aromatic acetal polymer, the photosensitive composition may optionally contain a variety of other ingredients such as colorants, stabilizers, exposure indicators and surfactants. Particularly useful colorants are pigments, including phthalocyanine, anthraquinone and quinacridone pigments. Useful amounts of pigment are from about 1 to about 20 percent by weight of the photosensitive composition, more preferably from about 2 to about 12 percent by weight and most preferably from about 4 to about 8 percent by weight. Effective stabilizers include both organic and inorganic acids, preferably citric, phosphoric, ascorbic, oxalic or tartaric acids. Useful amounts of acid are from about 2 to about 6 percent by weight of the photosensitive composition, more preferably from about 2.5 to about 5 percent by weight, and most preferably from about 3 to about 4 percent by weight. Useful exposure indicators are dyes which are pH sensitive and which do not couple with diazonium compounds. Examples of such dyes include eosin, azobenzene, Victoria Blue, 4-phenylazo diphenylamine, methyl violet and phenolphthalein. Useful amounts of the dye are from about 0.01 to about 3 percent by weight of the photosensitive composition, more preferably from about 0.05 to about 2 percent by weight, and most preferably from about 0.1 to about 1 percent by weight. Useful surfactants include fluorocarbon surfactants, and silicone surfactants. The surfactant is used in an amount of from about 0.005 to about 6 percent weight of the photosensitive composition, more preferably in an amount less than about 2 percent by weight, and most preferably less than about 1 percent by weight.
In a particularly preferred embodiment, the diazo resin used in the photosensitive composition of this invention comprises a condensation product of 3-methoxy-4-diazodiphenylamine sulfate and methoxymethyl-substituted diphenyl ether and salts thereof.
The fluorinated aromatic acetal polymer may advantageously contain photopolymerizable ethylenically unsaturated groups, photocrosslinkable groups or combinations thereof. For this embodiment, in addition to a diazo resin, it is advantageous that the photosensitive composition further comprises a photoinitiator, or photosensitizer or combination thereof in order to facilitate photopolymerization or photocrosslinking of the reactive groups.
Such diazo photopolymer hybrid compositions are well known in the art, as described in U.S. Pat. No. 4,687,727 and U.S. Pat. No. 4,845,009 the disclosures of which are incorporated herein by reference. U.S. Pat. No. 4,687,727 describes photosensitive hybrid compositions containing diazo resins together with photopolymerizable (meth) acrylated resins. Photopolymerizable (meth) acrylate groups can be incorporated into the fluorinated aromatic acetal polymers by various known methods, including reaction with compounds containing both an isocyanate group and a methacrylate group, such as 2-isocyanatoethyl methacrylate. Reaction of the isocyanate group with a hydroxy group on the polymer results in the introduction of photopolymerizable methacrylate groups.
In a similar manner, reaction of the isocyanate group of m-isopropenyl-xcex1, xcex1-dimethyl, benzyl isocyanate (m-TMI, available from Cytec Corp) with a hydroxy group on the fluorinated aromatic acetal polymer results in the introduction of photopolymerizable isopropenyl groups. Photoreactivity of these compositions is enhanced by the addition of one or more photoinitiators for free radical polymerization, which are well known in the art. Further enhancement in photoreactivity may be achieved by the addition of (meth) acrylated monomers and oligomers, which may copolymerize with the photoreactive fluorinated aromatic acetal polymers.
U.S. Pat. No. 4,845,009 describes photosensitive hybrid compositions containing diazo resins together with polymers containing photocrosslinkable dimethylmaleimide groups. In this case, photoreactivity is enhanced by the addition of photosensitizers, notably thioxanthone derivatives. Photocrosslinkable dimethylmaleimide groups can be incorporated into the fluorinated aromatic acetal polymers by various known methods, including reaction with compounds containing both a dimethylmaleimide group and an aldehyde group or aldehyde derivative, such as an acetal. Examples of such compounds, which contain both dimethylmaleimide groups and acetal groups, as well as their reaction with polyvinyl acetals, are described in U.S. Pat. No. 6,087,066, which is incorporated herein by reference.
In such diazo photopolymer hybrid compositions, the diazo resin is used in amounts of from about 1 to about 18 weight percent, preferably from about 2 to about 10 weight percent. The acetal polymer is used in amounts of about 10 to about 70 weight percent of the photosensitive composition, preferably from about 20 to about 65 weight percent.
The imageable member of this invention comprises a support and the photosensitive composition of this invention which is applied to the support. The photosensitive composition is coated onto the support by coating methods well known to those skilled in the art, such as roll coating, gravure coating, spin-coating or whirling. Roll coating and gravure coating are particularly preferred. Methods known to those of skilled in the art used for coating supports with imageable or photosensitive compositions, such as those described in European Patent Application EP 909 657 (incorporated herein by reference), may be used.
For the preparation of printing plates, such as lithographic printing plates, the photosensitive composition is applied, preferably by coating techniques, onto a suitable support such as a metal, polymeric film, ceramic, or polymeric-coated paper using conventional procedures and equipment. Suitable metals include aluminum, zinc or steel, but preferably, the metal is aluminum. A most preferred support is a mechanically and electrochemically grained (multi-grained) and sulfuric acid anodized aluminum sheet. Such elements are generally known as lithographic printing plate precursors, but other useful elements include printed circuit boards. Typically, an aluminum substrate is first grained by brushing in dry condition, by brushing with an abrasive suspension, by electrochemical graining, for example in a hydrochloric acid electrolyte or combinations thereof (multi-grain). The grained plates, which optionally have been subjected to an anodic oxidation in sulfuric or phosphoric acid, are then subjected to a hydrophilizing treatment, preferably in aqueous solutions of polyvinyl phosphonic acid or phosphoric acid. Such substrate pretreatments are well known to those of skill in the art. The plate may also be post anodically treated with materials such as silicate.
The imageable member of this invention may be imaged by exposure to suitable electromagnetic radiation, as is well understood by those of ordinary skill in the art. For example, the imageable member may be imaged using radiation in the UV to IR range. The imageable member may also be imaged using xe2x80x9ccomputer-to-platexe2x80x9d (CTP) imaging applications. Such systems utilize digitized image formation, as stored on a computer disk, compact disk, computer tape or other digital information storage media, or information that can be provided directly from a scanner, that is intended to be printed. The bits of information in a digitized record correspond to the image elements or pixels of the image to be printed. This pixel record is used to control the exposure device, that is a modulated laser beam. The position of the laser beam can be controlled using any suitable means known in the art, and turned on and off in correspondence with pixels to be printed. The exposing beam is focused onto the imageable member of this invention.
Laser imaging may be carried out using any moderate or high-intensity laser diode writing device. During operation, the element to be exposed may be placed in the retaining mechanism of the writing device and the write beam scanned across the element to generate an image. A laser printing apparatus may be used that includes a mechanism for scanning the write beam across the element.